FIG. 1 shows main structure and operating manner of a conventional air compressor. Power produced by a motor 16 is transferred to a piston rod 12 via an idle wheel 22, so that the piston rod 12 moves in a crankcase 14 in circular motion and a piston head 24 of the piston rod 12 moves in a cylinder 18 in reciprocating motion. The cylinder 18 has a cylinder head 10 provided with a top cover 30. The top cover 30 is formed of an air inlet 26 and an air outlet 28, both of which have a check valve mounted thereat. When the piston head 24 moves downward, external air is guided into the cylinder 18 via the air inlet 26 and the check valve (not shown) mounted thereat. The check valve functions to prevent air from flowing back to external environment via the air inlet 26. When the piston head 24 moves upward, it compresses the air guided into the cylinder 18. The compressed air flows through another check valve 20 mounted at the air outlet 28 and passes the air outlet 28 into an air storage tank connected to the air compressor. The check valve 20 functions to prevent air from flowing back from the air storage tank into the cylinder 18.
Since the conventional air compressor has air inlet and air outlet that all are provided on the cylinder head, the cylinder and the cylinder head are subject to temperature rise when they have been moving over an extended period of time. The heated cylinder and cylinder head results in relative increase of temperature of the air guided into the cylinder and accordingly lowered compression efficiency. Moreover, the temperature rise also causes thermal expansion of the cylinder to increase noises and errors during operation thereof, and decrease the usable life of the cylinder.
It is therefore a primary object of the present invention to solve the above-mentioned problems by providing an improved oil-free air compressor, in which only the air outlet is provided on the cylinder head. The air compressor of the present invention has an air inlet that is provided on a lateral end of the crankcase, so that external air is guided into the air compressor via the lateral air inlet to pass through a check valve on the piston head and into the cylinder, at where the air is compressed with the piston. The compressed air is then discharged from the cylinder to the air storage cylinder via the only one air outlet provided on the cylinder head. With these arrangements, air guided into the cylinder is always external cold air that effectively reduces the temperature of the cylinder and the cylinder head to increase the compression efficiency and the usable life of the cylinder.
Another object of the present invention is to provide an improved oil-free air compressor that has an air inlet provided at a lateral open end of the crankcase thereof, enabling the air inlet to have increased dimensions large enough for a filter to removably mount therein to screen off impurities in the external air entering into the cylinder via the air inlet.
A further object of the present invention is to provide an improved oil-free air compressor that has a cylinder head on which only an air outlet is provided, enabling the cylinder head and the piston to have reduced dimensions and therefore be more easily manufactured, assembled, maintained, and repaired.